Loud-speaking telephone system



Jan. 3, 1928.

1,655,028 R. F. STEHLIK LOUD SPEAKING TELEPHONE SYSTEM File March 1923 B Cr 2%? a mik Patented Jan. 3, 1928.

UNITED STATES PATENT OFFICE.

RUDOLPH F. STEI-ILIK, OF CHICAGO, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS,

T0 AUTOMATIC ELECTRIC INC, OF CHICAGO, ILLINOIS, A CORPORATION OF DELA- WARE.

LOUD-SPEAKING TELEPHONE SYSTEM.

Application filed March 14, 1923. Serial No. 624,886.

The present invention relates in general to loud speaking telephone systems, but is more particularly concerned with substation equipment for use in such systems: and the object of the invention may be said to be, broadly, the provision of new and improved auxiliary apparatus for use in connection with a telephone substation.

In the preferred form of the invention, means are provided whereby a loud speaking equipment may be substituted for the usual telephone equipment at the discretion of the subscriber. When a connection is estab lished, and the transmission proves unsatisfactory, or the subscriber finds it desirable to move about the room during the period of conversation, he may operate a key which cuts the auxiliary apparatus across the line and disconnects the ordinary receiver and transmitter. The receiver associated with the loud speaking equipment renders the incoming message audible throughout the room, while the transmitter associated therewith may be actuated by a voice of ordinary conversational volume emanating from any point in the room.

The object of the invention will be more fully pointed out hereinafter, reference being had to the accompanying drawing, which shows by means of the usual circuit diagrams sufiicient details of the apparatus embodying the principles of the invention to enable.

one familiar with the art to understand the same.

Referring to the drawing, A is an ordinary automatic substation having the usual talking, signalling. and impulse sending instrumentalities. The substation A is normally connected through the locking key K to the line switch C at the central oilice. In addition to the usual line conductors and 17 there is a test conductor 16, and a battery conductor 18 extended from the central oflice to the especially equipped substation.

The line switch C is of the well known rotary type, and can extend connections to the switches of an automatic telephone system.

The transmitter associated with the loud speaking equipment is indicated at T, while the receiver associated therewith is indicated at R. Repeating coils are indicated by reference characters R, R, R and R Vacuum tubes-of the well known type are indicated by reference characters 19 and 20.

The system having been described in general, a detailed description of its operation will now be given. For this urpose it will beassumed that station A is 1n talking connection with a second station (not shown). For the purpose of explanation it is immaterial whether station A is the calling or called station. for in either case the conductor 16, which leads to the associated test contact in the test bank of the connector will be grounded. We may further assume that the subscriber operates the locking key K. thus bridging winding 21 of repeating coil R across line conductors 15 and 17 in lace of the receiver and transmitter of su station A.

A further result of the operation of key K is the closing of a circuit from grounded test conductor 16, working contact and spr ng 14, relay 22 to battery. Relay 22 energizes and closes the filament circuit of vacuum tube 19 at armature 23. The filament circuit of vacuum tube is closed at armature 24, while the circuit of transmitter T is closed at armature 25. The resistances 26 and 27 are placed in series with their respective filaments in order that the latter may be operated from the standard central. oflice potential.

The operation of the receiver R will now be explained. The winding 21 of repeating coil R is in bridge of the line. Therefore the current flow in this coil will be controlled by the transmitter at the distant end of the line. The variations of current in winding 21 will induce like currents in winding 28, which will'fiow over a cricuit traceable from ground, winding 28, winding 29 and 32 of repeating coil R winding 31 of repeating coil R which represents an artificial line, to ground. The windings 29 and 32 are so connected that the current flowing in the above traced circuit will induce a current in winding of repeating coil R The latter winding is connected between battery and the in-put side of the vacuum tube 20, and the current induced therein will cause a variation of the grid potential. The receiver R tential.

being connected between ground and the plate of vacuum tube 20, the current flowing therein will vary in accordance with the current variation in winding 21 of repeating coil R. As a result of the fore oing, receiver R will reproduce the sounds spoken into the transmitter at the other end of the line. Because of the amplification afiorded by the vacuum tube 20 the volume of sound produced will greatly 'exceedthat normally obtained by the receiver of substat1on A.

The 0 eration of transmitter T Wlll now be explained. The diaphragm of the transmitter, responding to the sounds spoken into it at a distance, will vary the current flow in a circuit traceable from ground, transmitter T, armature 25 and its worklng contact, winding 33 of repeatingcoil It to battery. The current variations 1n this win-ding will cause like currents to be induced in the winding 34. This winding is connected between battery and the in-put SIdG of the vacuum tube 19, and the currents induced therein will cause variations of the grld po- It will be seen that the plate of vacuum tube 19 is connected to a point between the windings 29 and 32 of repeating coil R Therefore the current in the plate circuit will be divided; half passing through winding 29 and winding 28 of repeating coil R to ground, while the other half passes through winding 32 and winding 31 of repeating coil R to ground. The windings 28 and 32 are so connected that the current flowing in the above circuit will have no effect upon winding 30. This is the usual and well known anti-side-tone circuit arrangement. The current flowing in winding 28 of repeating coil R will vary inaccordance with the current flowing through transmitter T. Because of the amplification ofiered by the vacuum tube 19 the current value in the winding 28 will be greatly in excess of that in the circuit of transmitter T. A current, therefore, will be induced in winding 21 of a strength required to operate the receiver at the distant station.

When the conversation is completed the key K will be restored and the connection released in the usual manner. If an incoming call to station Ais released while the key K is in an operated position, the receiver R and the transmitter T will set up a side tone action, indicating to the subscriber at substation A that the calling party has released. This action is caused by the removal of the physical line, which unbalances the repeating coil R, thus causing the receiver and transmitter to interact and howl, and will cease when the ground is removed from the circuit of relay 22. i

While the invention is shown in connection with an automatic telephone system it is to be understood that it is equally applicable to other systems.

speaking apparatus with the line when a call is received, repeating coils for associating the two amplifiers with the line circuit, and an artificial line adjusted to balance the telephone line in talking condition to prevent side tone, whereby when the calling party hangs up a condition of unbalance will be set up causing the loud speaking transmitter and receiver to interact and howl.

2. In an automatic telephone system, a plurality of substations each comprising a telephone equipped with a calling device, a central oflice, automatic switches thereat responsive to manipulations of said calling devlce to extend a connection to another substation, loud speaking equipment comprising a transmitter, a receiver and two amplifier tubes associated with the substation, a key for substituting the loud speaking equipment for the telephone, and means for holding the extended connection intact while the loud speaking equipment is in use.

3. In a telephone system, a line, loud speaking apparatus comprising, a receiver, a transmltter, and receiving and transmitting amplrfiers, means for connecting said loud speaking apparatus with the line after a call 1s received, repeating coils for associat- 1ng the amplifiers with the line circuit, and means whereby when the calling party disconnects, the loud speaking transmitter and receiver will interact and howl to warn the called subscriber of this fact.

4. In a telephone system, a line provided with equlpment comprising a telephone transmitter, receiver and a call signal and also e nipped with a loud speaking apparatus 1nclu 1n g an amplifying receiver and an amplifylng transmitter, means for extending a connection to said line, a key for disconnectmg said equipment and for connectng the apparatus to the line when a call is received, and means responsive to the disconnection of the party calling for causing said recelver and transmitter to interact and howl to inform the called party of this fact so that he will restore the key to place this1 line in condition to receive subsequent ca s.

5. In an automatic telephone system, substations provided with ordinary transmitting and receiving apparatus and also with loud-speaking equipment comprising 4 a transmitter, a receiver and two amplifier tubes, means for substituting said equipment for said apparatus, a central exchange povided with switches for extending connections from calling to called stations, a pair of line conductors and a test conductor for connecting said stations with said exchange, and relay means opera-ted over said test conductor tor controlling the circuits of said loud speaking equipment.

6. In an automatic telephone system, substations provided with ordinary transmitting and receiving apparatus and also with loud speaking equipment comprising a transmitter, a receiver and two amplifier tubes, a key for substituting said equipment for said apparatus, a central exchange, a pair of line conductors and a test conductor for connecting said stations with said exchange, and a relay at said stations, operated over said test conductor for controlling the circuits of said loud speaking equipment.

7. In an automatic telephonesystem, a

substation provided with ordinary transmitting and receiving apparatus and also with loud speaking equipment including amplifier tubes, at central exchange, a pair of line conductors and a test conductor for connecting said station with said exchange, a relay at said station for controlling the circuits of said loud speaking equipment, and means for substituting said equipment for said apparatus and for connecting said relay with said test conductor to operate the same.

8. In an automatic telephone system, a substation provided with ordinary transmitting and receiving apparatus and also with loud s eaking equipment including amplifier tu es and a control relay, a central exchange, a pair of line conductors and a test conductor for connecting said station with said exchange, means for substituting said equipment for said apparatus and for connecting said control relay with said test conductor, and means operated by said relay for controlling the circuits of said loud speaking equipment.

9. In an automatic telephone system, a substation provided with ordinary trans mitting and receiving apparatus and also with loud speaking equipment including amplifier tubes, and a control relay, a central exchange, a pair of line conductors and a pair of control conductors for connecting said station with said exchange, means for substituting said equipment for said apparatus and for connecting said relay in circuit with said control'conductors, and means operated by said relay for controlling the circuits of said loud speaking equipment.

In witness whereof, I hereunto subscribe my name this 10th day of March, A. D.

RUDOLPH F. STEHLIK. 

